1. Field of the Invention
The present invention relates to a fixing device included in an image forming apparatus such as a copier, printer, facsimile machine, or the like, to fix an image carried on a recording medium onto it, a fixing method, and an image forming apparatus employing such a fixing device and an image forming method employing such a fixing method.
2. Description of the Related Art
In conventional fixing devices as disclosed in JP-2002-006656-A, JP-H06-230626-A, JP-H08-254913-A, and JP-H10-282830-A, when a recording medium is conveyed or passed through a fixing nip to exert fixing effect, there occurs a problem of creases and curls in the recording medium. Such a problem tends to occur easily with conveyance members such as a fixing roller, heat roller, pressure roller and the like, to convey a recording medium that are made thin or made to have a low heat capacity due to the recent trend for the low energy consumption. By making the conveyance member thinner, heat transfer speed in the width direction of the conveyance member decreases and temperature thereon varies, resulting in variations in the shape of the thermally expanded conveyance member in the width direction, whereby the conveyance property of the recording medium varies in the width direction and creases and curls occur to the recording medium.
As an aspect of the temperature variations in the conveyance member, there is a case in which temperature difference occurs between one side of the conveyance member in the width direction and another side thereof. Such a phenomenon occurs as follows.
When the conveyance member is driven to rotate for conveying the recording medium, in general, a mechanism to drive the conveyance member is provided at one end side in the width direction of the conveyance member. In such a case, when the driving mechanism acts on a heat absorbing side, the temperature at one end side of the conveyance member decreases faster than the temperature of another end side thereof, to thus vary the temperature.
It is known to use air to prevent excessive temperature rise of the fixing device. When, for example, air is blown from a first lateral side of the conveyance member to a second side, more heat is absorbed at the first side than the second. Therefore, the temperature at the one end side of the conveyance member decreases more than that of another end side thereof, to thus cause temperature variations.
Also even in such a case in which temperature difference occurs from one side to another in the width direction of the conveyance member, as described above, shape difference of the conveyance member due to the thermal expansion occurs in the width direction caused by the temperature difference. Then, when the recording medium is passed through the fixing nip, creases and curls are formed to the recording medium and the fixing property varies.
However, conventionally, no optimal technology has been disclosed capable of preventing creases and curls in the recording medium and variations in the fixing property, in view of the cases in which temperature difference occurs between one end side of the conveyance member in the width direction and another end side thereof.